Numbers 1:24(King James Version)Of the children of Gad, by their generations, after their families, by the house of their fathers, according to the number of the names, from twenty years old and upward, all that were able to go forth to war;

The tribe of Gad marched, along with that of Simeon, under the standard of Reuben; and it seems, on that account, to have been introduced in this order. The other tribes also, are here classed together according to their encampments, and the order of their subsequent march.